Glossary · Electrical engineering and control panels
Digital output
Also known as: DO, Discrete output, Binary output
German: Digitalausgang
In industrial control, a digital output is a controller output channel that switches between two states to drive devices such as relays, solenoid valves, indicator lights or contactor coils, implemented as a transistor or relay output.
- Control panels
In one sentence
A digital output switches between two states to drive relays, valves, lamps or contactor coils, as a transistor or relay output.
Example
The PLC sets a digital output to energize the solenoid valve that extends the clamping cylinder.
How it applies
- Engineering: Check output current, total current per module, load type (inductive loads need suppression) and behavior on controller stop. Outputs usually switch off on stop, which must lead to a safe state of the connected equipment, a Safe default.
- Commissioning: Forcing outputs for tests moves machinery. Do it only under controlled conditions, with the hazard area clear.
- Documentation: The I/O list shows each output with its device, tag and fail state. Service instructions for forcing outputs must include the necessary safety precautions.
Digital output vs. safety output
A standard digital output is not designed to perform a safety function on its own. Safety outputs of safety controllers include diagnostics such as test pulses and are used in safety functions.